Various styles of containers, including paperboard boxes, are known in the prior art for containing a variety of products. Cut poultry pieces, for example, are frequently packed in a paperboard container, and sometimes the poultry pieces are packed with ice. These containers are generally referred to as poultry trays, and are usually made from a unitary blank of corrugated paperboard, which may be treated on one or both sides with wax or other material to impart rigidity and resistance to water degradation.
Conventional paperboard containers are configured for either machine set up or manual set up, and generally are either rectangular or octagonal in plan view, with four sides or eight sides, respectively. An example of a prior art eight-sided container is disclosed in applicant=s prior U.S. Pat. No. 5,752,648. The embodiment shown in FIGS. 1 and 3 of that patent is configured for manual set up, and has three overlapping end panels 18, 24 and 24, with notches 30 formed in the top edges of the two end panels 24, and a roll-over flap 34 foldably joined to the top edge of end panel 18 by short narrow webs formed between transverse cuts or relief slits 37 extending in spaced relationship transversely across cut lines 36 and 38, and interrupting the cut lines. Pairs of short cuts or slits 39 are formed in the webs parallel to the cut lines 36 and 38, but spaced from one another on opposite sides of the cut lines a distance approximately equal to the combined thickness of the three overlapped end panels. The slits 39 promote bending or folding of the webs along fold lines extending through the slits.
To erect the container, the two end panels 24 are folded inwardly into overlapping registry with one another, and the end panel 18 is then folded into overlapping relationship with panels 24. The roll-over flap 34 is then folded inwardly and downwardly over the upper edges of the panels 24, causing the webs to drop into notches 30, and the upwardly extending portions of panels 24 on opposite sides of the notches to project upwardly through the cuts formed by the cut lines 36 and 38. The relationship of the relief slits 37 and cut lines 36 and 38 causes a “heel” to be formed on the edge of the roll-over flap, and this heel produces an over-center effect when the roll-over flap is folded over the panels 24. The heel engages against the inner surface of the innermost end panel 24 to keep the roll-over flap in its folded position, and thereby maintains the container in erected condition.
While the arrangement disclosed in U.S. Pat. No. 5,752,648 provides a simple and effective self-locking system for holding the container in its erected condition, the thickness of the material of the webs causes them to take a slightly “rounded over” shape as they are pulled down into the notches 30, and they tend to exert a pull on the roll-over flap in a direction to disengage it. Additionally, in order to insure that the webs and related components can be operatively engaged with one another, specific dimensional relationships are maintained between the distance from the bottoms of the notches to the bottom of their associated panels 24, and the distance which the relief slits 37 extend above the cut lines 36 and 38, i.e., the length of the relief slits is slightly exaggerated, contributing to a “loose” fit between the components of the self-locking arrangement.
A solution to this was offered in applicant's co-pending patent application, published Mar. 13, 2003, under publication number US-2003-0047592-A1. The container disclosed in this application is similar to that used in U.S. Pat. No. 5,752,648, but is modified to achieve a tighter fit between components of the self-locking arrangement and provide a more reliable interlocking of the components. More specifically, the container disclosed in US-2003-0047592-A1 has a bottom wall, opposite side walls, and opposite end walls, with means on the end walls that interlock to hold the container in its erected condition. The container is made from a unitary corrugated paperboard blank having a bottom panel that forms the bottom wall, opposite side wall panels foldably joined to opposite sides of the bottom panel and that form the side walls, and end panels extending from opposite ends of the bottom panel and side wall panels, respectively, at least some of the end panels overlapping to form the end walls. At least one notch is formed on an upper edge of at least one of the end panels, and a roll-over flap is formed on an upper edge of another end panel, in positions to interlock with one another when the end panels are folded into operative relationship with one another to form an erected container.
In particular, the self-locking structure in US-2003-0047592-A1 has a plurality of notches formed in the edge of at least one end panel, defining at least one tab projecting upwardly from the edge of the panel, and the roll-over flap is foldably joined to its associated end panel by webs formed between a cut line that lies parallel to the fold for the roll-over flap, and relief slits that extend transversely across the cut line. The webs are adapted to lie in the notches, with said at least one tab projecting into a slot formed by the cut line when the roll-over flap is folded inwardly and downwardly over the end panels. The webs are at least partially crushed on the side thereof that faces downwardly in the notches so that they lie substantially flat in the notches. In addition, the dimensional relationships of the self-locking arrangement are made tighter to affect a tighter fit between components, producing a more reliable interlock. Specifically, the distance from the bottom of the notches to the bottom of their associated panels is made smaller than in a tray having a conventional self-locking arrangement, and the length of the relief slits is also made smaller.
However, the prior self-locking roll-over flap as disclosed in the co-pending patent application identified above, and as illustrated in FIGS. 1 and 2 attached hereto, may come unlocked under stress, e.g., when force is exerted against the side walls by product in the container, causing the package to partially disassemble.
Accordingly, there is need for a self-locking arrangement that provides a tight, secure fit between components, and that does not come unlocked under stress, insuring that a container incorporating the arrangement reliably remains in its erected condition.